AcWing 907. interval coverage

 

// 1. in accordance with all sections of the left point from small to large
 // 2 from front to back in order to enumerate each interval
 // First select the rightmost endpoint can cover the left end point of the interval among the right end point
 // in all energy covering the interval among the start, select the right end of the maximum interval
 // after finished selecting the start point is updated to the maximum value of the right 
#include <the iostream> 
#include <algorithm>
 the using  namespace STD;
 const  int N = 100010 ;
 int n-;
 struct {the Range
     int L, R & lt;
     BOOL  operator <( const the Range W is &) const {
         return L < Wl of the;
    }
} range[N];
int main() {
    int st, ed;
    scanf("%d%d", &st, &ed);
    scanf("%d", &n);
    for (int i = 0; i < n; i ++ ) {
        int l, r;
        scanf("%d%d", &l, &r);
        range[i] = {l, r};
    }
    Sort (Range, Range + n-);
     int RES = 0 ;
     BOOL Success = to false ;
     for ( int I = 0 ; I <n-; I ++ ) {
         int J = I, R & lt = - 2E9;
         // find all left on the left, right interval start point is the maximum number 
        the while (J <n-&& range [J] .L <= ST) {
            r = max(r, range[j].r);
            j ++ ;
        }
        if (r < st) {
            res = -1;
            break;
        }
        res ++ ;
        if (r >= ed) {
            success = true;
            break;
        }
        st = r;
        i = j - 1;
    }
    if (!success) res = -1;
    printf("%d\n", res);
    return 0;
}